Work machines such as, for example, track-type tractors and other heavy construction, agriculture, and mining machines, are used to perform many tasks. To effectively perform these tasks, the work machines require a power source that provides significant power to a drive arrangement. The power source may be an engine such as, for example, a turbine engine, diesel engine, gasoline engine, or natural gas engine operated to generate a torque output at a range of speeds. The drive arrangement may include individual motors driven by the power source and associated with individual traction devices of the work machine. These individual motors must be sized to transmit the entire torque output of the power source to the associated traction device, for if one traction device slips due to unfavorable traction conditions, the entire torque output of the engine will be absorbed by the non-slipping traction device. In addition, due to regenerative forces, it may be possible to load a single motor and associated traction device with the entire torque output of the power source and an additional amount of torque that is being regenerated from a traction device located on an opposite side of the work machine. As a result of these occasional high-torque and/or high power loading situations, these motors are typically oversized for a majority of the work machine operation. In addition to the high component cost of the oversized motors and related packaging issues, operation of these oversized motors during low-torque loading conditions is inefficient.
One attempt to reduce the cost and inefficiencies associated with oversized drive arrangements is described in U.S. Pat. No. 5,168,946 (the '946 patent) issued to Dorgan on Dec. 8, 1992. The '946 patent describes an electric drive system having first, second, and third electric motors connected via left and right combining gear sets to respective left and right vehicle tracks. To propel the vehicle in low range operations (e.g., low speed, high torque), the first and second motors are energized, while the a brake is applied to the third motor. To propel the vehicle in high range operations (e.g., high speed, low torque), all three motors are energized. Regeneration of power may be available during high range operations. The use of three motors, rather than two, in high range operations results in a reduction of motor sizes.
Although the electric drive system of the '946 patent may reduce some of the cost and inefficiency associated with oversized motors, it may be operationally limited and inefficient. In particular, the third motor may only be used during high range operations. The largest amounts of torque are generated during low range operations that involve steering or traction loss. Because only two motors of the '946 patent propel the vehicle during low range operations, the two operational motors must still be oversized to accommodate the associated high torque loads. In addition, regeneration is most effective during steering operations of the vehicle, which most often occur during low range operation. Because regeneration is only available during high range operations of the vehicle described in the '946 patent, the electric drive system may lack efficiency.
The planetary drive arrangement of the present disclosure solves one or more of the problems set forth above.